Fault detector for igniter testing using high frequency noise

ABSTRACT

A method and apparatus for detecting faults in electrical resistance type igniters, particularly igniters of silicon carbide or the like, employs techniques wherein an operational voltage is applied to the igniter to cause the generation of high frequency noise by a defective igniter. The high frequency noise developed across a defective igniter is sampled by a circuit which includes a high frequency transformer which couples the high frequency noise sampling to a high pass filter. The high frequency noise is passed through the high pass filter and applied to an amplifier, and the amplified noise is presented to a signal level detector in the form of a comparator circuit. The comparator circuit is provided with a reference level to desensitize the comparator circuit with respect to signals below the reference level, and the output of the comparator circuit is received by a memory circuit. The memory circuit in turn controls an alarm circuit which emits a signal to indicate a faulty condition of the igniter undergoing test.

United States Patent [1 1 Pfouts FAULT DETECTOR FOR IGNITER TESTINGUSING HIGH FREQUENCY NOISE John Richard Pfouts, Mount Victory, Ohio [75]Inventor:

[73] Assignee: Whirlpool Corporation, Benton Harbor, Mich.

[22] Filed: Apr. 25, 1974 [21] App]. No.: 463,963

Primary ExaminerStanley T. Krawczewicz Attorney, Agent, or FirmHill,Gross, Simpson, Van Santen, Steadman, Chiara & Simpson [4 1 Sept. 16,1975 1 ABSTRACT A method and apparatus for detecting faults inelectrical resistance type igniters, particularly igniters of siliconcarbide or the like, employs techniques wherein an operational voltageis applied to the igniter to cause the generation of high frequencynoise by a defective igniter. The high frequency noise developed acrossa defective igniter is sampled by a circuit which includes a highfrequency transformer which couples the high frequency noise sampling toa high pass filter. The high frequency noise is passed through the highpass filter and applied to an amplifier, and the amplified noise ispresented to a signal level detector in the form of a comparatorcircuit. The comparator circuit is provided with a reference level todescnsitize the comparator circuit with respect to signals below thereference level, and the output of the comparator circuit is received bya memory circuit. The memory circuit in turn controls an alarm circuitwhich emits a signal to indicate a faulty condition of the igniterundergoing test.

10 Claims, 5 Drawing Figures VOLTAGE SUPPLY 5s r 3 Ill IGNITERASSEMBLY54 T TO AC POWER 72 SOURCE 52 PATENTEB 3E? 975 SHEET 1 [IF 2Fig. 2

SIGNAL HIGH PASS AMPLIFIER LEVEL MEMORY ALARM FILTER DETECTOR CIRCUITCiRCUIT 1 f as so +62 e4 4 6 HIQH FREQUENCY TRANSFORMER 78 2 j LOWVOLTAGE Ac POWER IGNITER POWER SUPPLY, sou RcE ASSEMBLY RESETfi CONTROLCIRCUITRY PATENTEU SEP 1 61975 SHEET 2 UP 2 mm mumnom mw om u E.

b?! 3 imam? $529 FAULT DETECTOR FOR IGNITER TESTING USING HIGH FREQUENCYNOISE CROSS REFERENCE TO RELATED APPLICATIONS This application isrelated to a United States patent application by Edward Getz andClifford DeSchaaf entitled, Fault Detector for lgniter Testing, U.S.Pat. application Ser. No. 463,962, filed on the same date as the presentapplication, and assigned to the assignee of the present invention.

BACKGROUND OF THE INVENTION 1, Field of the Invention This inventionrelates to resistance testing techniques, and more particularly totechniques for testing an electrical resistance type igniter which maybe employed as a pilot for igniting the fuel for a gas burner.

2. Description of the Prior Art I Burner units have long utilized anelectrical resistance type ignition element in an electrical ignitionsystem, and such ignition systems have been applied to clothes dryers.Many gas dryers use an igniter which, for example, may be of the typedisclosed in US. Pat. No. 3,372,305 granted Mar. 5, 1968, made ofsilicon carbide or like material which is generally very fragile.Consequently, a serious problem encountered in utilizing such ignitersin a clothes dryer is the large number of damaged or defective ignitersappearing in newly manufactured appliances. This quality control problemis compounded by the fact that a cracked, or otherwise damaged ordefective, igniter may perform normally for short initial periods ofdryer operation and its faulty condition may go undetected duringinitial tests performed prior to crating and shipping of the dryer.However, in many instances such a faulty igniter will fail soon afterthe dryer has been installed for home use. Therefore, it is highlydesirable to provide a reliable, relatively inexpensive, and easy-to-usetest technique, including test method and apparatus, for detectingdefective igniters so as to permit their timely replacement.

The article Noise-Performance in Tin Oxide Resistors," by J. G. Curtisappearing in the Nov. 10, 1961 issue of the periodical Electronicsdiscloses the phenomenon of noise generation by substandard resistors,and the utilization of that noise to detect certain types of defects infilm resistors.

US. Pat. No.3,727, l 33 discloses noise measurement as an indication ofdefect in a tested device, such as a DC generator.

The detection of X-rays is utilized in a testing technique in US. Pat.No. 3,761 ,720 to determine faults in a Van de Graaff generator.

US. Pat. No. 3,102,231 discloses a noise testing I technique in whichwhite noise is supplied to a system under test to provide a responsewhich is indicative of the status of the tested system.

Other publications concerning the utilization of noise testing anddetection teehniques may be of interest and include the article NoiseVoltage Measurement in Low Impedance Elements," appearing in the May 28,1958 issue of the periodical Electronic Design and US. Pat. No.2,820,945.

SUMMARY OF THE INVENTION The primary object of the invention, asindicated above, is to provide a new and improved method and apparatusfor testing electrical resistance type igniters for operational faultsor defects. l

A more specific object of the invention is to provide inexpensive,reliable, and easy-to-use techniques for testing such igniters.

According to the invention, an igniter is connected through test circuitapparatus to an operational volt age. When mounted in its operatingposition on a burner, the igniter may also be connected in circuit withthe gas valves of the burner in a manner such as illustrated by Alvin J.Elders in his US. Pat. No. 3,597,139, issued Aug. 3, 1971 and assignedto Whirlpool Corporation. The inclusion of the gas burner circuitry inthe test circuit does not interfere with the operation of the faultdetection apparatus, as will be appreciated from the detaileddescription below.

Upon energization by an operational voltage, for example that availablefrom a commercial volt alternating current (AC), 60 Hz source, adefective igniter produces noise of a higher frequency than theoperational voltage, and this higher frequency noise (referred to hereinas high frequency noise) together with the operational voltage noise issampled by a circuit ineluding a high frequency transformer whichcouples a noise sampling to a high pass filter where the opera tionalvoltage wave is substantially blocked. The signal passed by the highpass filter is then amplified and fed to a signal level detector. Thesignal level detector comprises a comparator circuit which compares thelevel of the amplified high frequency noise signal with a referencelevel. When the noise level is above the reference level, the comparatorcircuit provides output pulses which are fed to a memory circuit.

The memory circuit supplied current to a driver which energizes a greenindicator lamp when the noise level is below the reference level andsupplies current to a driver which energizes a red" indicator lamp whenthe noise level is above the reference level.

The fault detectoris provided with a low voltage power supply and apreset circuit is connected to the memory circuit to ensure operation ofthe green indica tor lamp initially when the low voltage power supply isturned on. i

As indicated above, cracks or other defects or faults in silicon carbideigniters or igniters of a like material are difficult to detect byvisual observation; however, defective igniters respond, to theapplication of operational voltages by generating high frequency noise.Several theories have been proposed as to the cause of this phenomenon,including noise generation due to arcing or corona discharge, but noneof these theories have been substantiated. Nevertheless, the method andapparatus disclosed herein fulfill the objects of the invention andprovide an accurate test of the operational integrity of an igniter.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantagesof the invention, its organization, construction, and operation will bebest understood from the following detailed description of embodimentsof the invention taken in conjunction with the drawings, of which:

FIG. 1 is a pictorial representation of an igniter fault detectorconnected to a gas burner component of a clothes dryer (not shown);

FIG. 2 is a schematieblock diagram of. the test apparatus of the presentinvention and also serves as a flow diagram for the test procedure ofthe present invention;

. FIG. 3 is a schematic circuit diagram of thc.circuit .illustrated inblock form in FIG. 2;

FIG. 5 is a schematic diagram of a portion of the apparatus circuitillustrated in FIG. 3, particularly showing theaddition of an audiblealann device, such as a buzzer.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a test setup for testing an igniter is generally illustrated at 10. A clothesdryer gas burner component assembly 12, such as disclosed in theaforementioned Elders US. Pat. No. 3,597,139, having an electricalresistance igniter 14 to be tested is connected to test equipment 16 byway of a cable 18. It should be noted here that the presence of the gasburner circuitry in the test circuit with the igniter has no effect onthe test; and that the harness or cable 18 may include conncctions tothe terminals of the gas burner assembly, or may simply provideconnections directly to the igniter 14. As shown, the cable 18 isadapted for connection to the gas burner terminals at a quick releaseconnector 50. Although not illustrated in the drawing, the gas burnerassembly 12 may be mounted within the housing of the dryer prior totesting of the igniter and remain in the dryer during actual testing ofthe igniter.

The test unit or equipment 16 comprises a case, which may be of metal,having a pair of sidewalls 20 and 22, a bottom wall 24, a top wall 26, afront wall or console 28 and a rear wall (not shown) through which anelectrical supply cord (not shown) may extend for connection to acommercial power supply, such as a l2()'VAC, 60 H7. supply. I

As illustrated in the drawing, the test unit 16 may be provided with acarrying handle 32 attached to the top wall 26, and the sidewalls 20 and22 may be provided with cooling louvers as illustrated at 34.

The front console 28 includes a green indicator lamp 36 for indicating adefect-free or sound igniter, a red indicator lamp 38 for indicating adefective or otherwise faulty igniter, a power-on/off switch 40 and acorresponding indicator lamp 42, a test switch 44, and access to anadjustable potentiometer 46, as will be understood from the descriptionwhich follows.

As shown in FIG. 1, the cable 18 is connected to the test unit 16 by aconnector 48 and is connected to the igniter 14, or to the igniter andthe gas burner circuitry, by a connector 50 as will be well understoodby those skilled in the art.

Referring to FIG. 2, an alternating current (AC) power source 52 isschematically illustrated as being connected by a power cord 30 to anigniter assembly 54, which may be installed in a gas burner assembly,and to a low voltage power supply 56. The low voltage power supply maybe a source of controlled voltage derived from or actuated by the source52; or may be, for

example, a direct current (DC) voltage source such as a pair ofbatteries. In the latter case the low voltage source would, of course,be independent from AC power source 52. In any event, such low voltagesourees'are well known in the art and will not be treatedinlfurther-detail herein;

The igniter assembly 54 holds the igniter 14 to be tested, and includeselectrical terminals providing an electrical connection between theigniter 14 and the AC power source. The igniter is electricallyconnected via igniter assembly 54 to a high frequency transformer 78 forsampling the high frequency noise signal emitted by-a faulty igniterunder test and coupling that signal to a high pass filter 58.

Upon the application of an operational voltage to a defective igniterthe igniter will generate high frequency noise which is coupled to'signal detecting means'including the high pass filter as indicatedabove. The high pass filter 58 (FIGS. 2 and 3) separates the highfrequency noise from the 60 Hz line frequency and passes the noisesignal to an amplification means 60 and a signal level detector 62 bothof which are also included in the signal detecting means.

The signal level detector 62 shown in FIG. 3 is a comparator circuitwhich includes means for providing an adjustable reference level todesensitize the circuit to signals below the reference level. Thus asensitivity adju'stment is provided for the test equipment to minimizethe rejection of igniters which are free from defects such as to besatisfactory for use with a gas burner.

The comparator circuit or signal level detector 62 is connected tosignal means including a memory circuit 64 which is conditioned to afirst state in response to detection by the comparator circuit of anoise level above the reference level and to a second state in responseto detection by the comparator circuit of a noise level which is belowthe reference level. The memory circuit 64 is connected to an alarmcircuit or lamp and driver circuit 66 which includes a pair of driversand indicator means for example, a pair of corresponding lamps (36 and38 in FIG. 1) for indicating the operational condition of an igniterundergoing test. The memory circuit and drivers together constituteswitching means for controlling the response of the lamps.

Referring to FIG. 3, a schematic circuit diagram of a preferredembodiment of the invention is illustrated in which an igniter assembly54 including an igniter l4 undergoing test is shown connectedto analternating current power source 52 by way of a pair of conductors and72 and a test switch 44. A capacitor 68 is connected across theconductors 70 and 72 as a filter, or partial filter, for removing linenoise from the commercial supply wavefonn. The power-on/off switch andthe corresponding indicator lamp have not been illustrated in detailsince one skilled in the art would readily appreciate the connection ofthese elements. Upon placing'the power switch 40 in the on' position, acontrolled low voltage power supply is made available and applied to thetest circuit at the terminals 71 and 73 in preparation fora test. Also,closing of the switch 40 provides power to the test switch 44.

Upon closing of the test switch 44, an operational voltage is applied tothe igniter under test and, if the igniter is faulty, high frequencynoise will be generated by the igniter.

A high frequency or untuned radio frequency transformer 78, whichincludes a primary winding 76 connected in series with the igniter byway of a conductor 74 and by way of the power supply conductor 74 and asecondary winding 80 electrically connected to the high pass filter 58,serves to sample the high frequency noise generated by the igniter, andcouples this sampling to the high pass filter. The high pass filter 58comprises a capacitor 82 and a resistor 84 and is effective to separatethe high frequency noisesampling from the 60 Hz line frequency.

The high pass filter 58, in particular the junction between thecapacitor 82 and the resistor 84 is connected to the amplification means60. More specifically, the junction 84a is connected to thenon-inverting input 86 of an operational amplifier 87. The invertinginput 88 of the operational amplifier 87 is connected to ground by wayof a resistor 90 and to the output 92 of the operational amplifier byway of a resistor 94. A negative potential is supplied to theoperational amplifier 87 by way of a conductor 101 and a positivepotential is supplied to the operational amplifier 87 by way of aconductor 100. A resistor 96 and a capacitor 98 are employed tofrequency compensate the operational amplifier 87, a technique wellknown to those skilled in the art. The amplification means 60 amplifiesthe high frequency noise received by way of the high pass filter 58 andhas its output 92 connected to the inverting input 104 of an operationalamplifier 105 by way of a resistor 102. The operational amplifier 105receives a negative potential by way of a conductor 110 and a positivepotential by way of a conductor 112, and a resistor 114 and a capacitor116 are employed to frequency compensate the operational amplifier 105in the same manner as was done with the operational amplifier 87.

A variable voltage divider comprising the potentiometer 46 and aresistor 108 is connected between the negative supply conductor 110 andground and includes a junction connected to the non-inverting input 106of the amplifier 105. This variable voltage divider provides a referencelevel to the amplifier 105 and functions to desensitize the circuit withrespect to signals below the reference level. If the signal level at theinput 104 is below the reference level atthe input 106 the comparisonprovided by the amplifier 105 results in a first output signal at theoutput 1 18 of the operational amplifier 105, and if the signal level atthe input 104 is above the reference level at the input 106 a secondsignal is provided at the output 118. i

The output 118 is connected to an inverter 120 in the form of a NANDgate which inverts the output signal of the operational amplifier 105and presents the inverted signal to a NAND gate 122 which is one ofapair of NAND gates 122 and 124 cross coupled as is well known in theart. The NAND gates 122 and 124 comprise what is known in the art as alatching circuit. All these NAND gates 120, 122, and 124 are powered ata junction A from the low voltage power supply 56, and the gates areprotected from exposure to potentially damaging voltages which exceedthe capacity of the gates by the grounded diodes 144 and 146electrically connected to gate inputs at junctions B and C respectively.

An inverted signal which represents a high frequency noise level belowthe reference level causes the memory circuit 64 to assume a statewherein the gate 122 is open and the gate 124 is closed. In this state,a driver transistor 132 having an emitter-base circuit including aresistor 130, is forward biased and rendered conductive to energize thegreen indicator lamp 36. The memory circuit is responsive toinvertedsignals of the opposite character (where the high frequencynoise level is above the reference level) to open the gate l24 and closethe gate 122, thereby effecting a forward bias on a driver transistor,134, which has its base connected to the gate 124 by way of a resistor131, to energize the red indicator lamp 38 to indicate a defectiveigniter.

As indicated in FIG. 2, the low voltage power supply block 56 includes apreset circuit. In FIG. 3, this preset circuit is illustrated ascomprising a resistor 126 and a capacitor 128 connected in series acrossthe low voltage supply lines and having the junction between theresistor and the capacitor connected to an input of the gate 124. Uponapplication of low voltage potentials to the terminals 71 and 73, thenegative potential shift at this junction causes the memory circuit 64to assume the first-mentioned state wherein the lamp 36 is energized.

Referring to FIG. 4, an inductor 136 is illustrated as connected in thecircuit in place of the radio frequency transformer 78. The inductorcould be, for example, l0 turns of No. 14 tinned copper wire l /s longand 4 inches I.D. Such an inductor would generate only a limited amountof 60 Hz nuisance signal, would generate no heat, and would not burn outunder short circuit conditions. The preferred embodiment employing aradio frequency transformer as illustrated in FIG. 3 achieved the bestresults. In the preferred embodiment a primary winding of 10 turns ofNo. l4 tinned copper wire, 1%; long and /4 inches [.D. and a secondarywinding of 12 turns of No. 14 tinned copper wire,

1% long and inches ID. was used; and, with these specifications, an evenlarger signal was processed to the filter, there was less 60 Hz nuisancesignal generated and less 60 Hz nuisance signal coupled to the amplifier60. In addition, the transformer generated no heat, and would not burnout under short circuit conditions; and the amplifier switching circuitswere advantageously isolated from the power lines.

Referring to FIG. 5, it may be advantageous in certain applications toutilize an audible alarm in conjunc tion with, or in place of, theindicator lamp 38. In FIG. 5, a buzzer 138 is connected in series withthe lamp 38 to operate and to provide an audible alarm in response todetection of a high frequency noise level by the test equipment abovereference level.

In addition to the aforementioned component specifications, thefollowing table sets forth component values and designations which werefound to provide accurate fault detection.

Reference Character Value. Designation 40 K pot 52 -120 VAC. 60 Hz 56 t6 VDC Power Source 81 98 I 16 0.00] pf.

87. I05 Operational Amplifier 96, I14 I50 ohm 120, I22, I24 DTI. NANDGates Although I have described my invention by reference to particularillustrative embodiments thereof, many sonably and properly be includedwithin the scope of my contribution to the art.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. Apparatus for testing an electrical resistance type igniter foroperational defects, comprising:

means for applying an operating voltage to the igniter to cause thegeneration of high frequency noise by the igniter if it is defective; I

an inductive impedance connected to the igniter for sampling signalsdeveloped by the igniter; filter means connected to said inductiveimpedance for passing high frequency noise;

amplifying means connected to said filter means for amplifying thesignal received therefrom;

signal level detector means connected to said amplifying means fordesensitizing the circuit with respect to noise signals below areference level; and

signal means connected to said level detector means and operative toindicate a defective igniter.

2. Apparatus according to claim 1, wherein said inductive impedancecomprises an inductor connected in series with said igniter.

3. Apparatus according to claim 1, wherein said inductive impedancecomprises a radio frequency transformer including a primary windingconnected to the igniter and a secondary winding connected to saidfilter means.

4. Apparatus for testing electrical resistance type igniters foroperational defects comprising:

means for connecting an igniter to an electrical sup ply for providingan operational voltage to the igniter, a defective igniter beingresponsive to the operational voltage to generate high frequency noise;

a radio frequency transformer for sampling signals developed across theigniter, said transformer including a primary winding connected to theigniter and a secondary winding;

a high pass filter connected to said secondary winding for passing highfrequency noise;

an amplifier connected to said high pass filter to amplify signalspassed thereby;

a comparator circuit including a first input connected to saidamplifier, a second input, and a reference level circuit connected tosaid second input, said comparator circuit being operable to providefirst and second signals when the signal level at said first input isabove and below, respectively. I the reference levels;

an inverter connected to said comparator circuit to invert the first andsecond signals;

first and second indicating means including first and second drivers andfirst and second lamps connected to respective drivers for identifyingdefective and sound igniters, respectively;

a latching circuit including a first input and first and second outputs,said first input connected to said inverter, said first and secondoutputs connected to said first and second drivers, respectively, saidlatching circuit being responsive to the inverted first-and secondsignals to operate said first and 'second drivers, respectively. 5.Apparatus for testing electrical resistance type igniters foroperational defects, comprising: means for 5 connecting an igniter to anelectrical supply for providing an operational voltage to the igniter, a

defective igniter being responsive to the operational voltage togenerate high frequency noise;

an inductor connected in series with the igniter to sample signalsdeveloped across the igniter;

a high pass filter connected to said inductor for passing high frequencynoise;

an amplifier connected to said high pass filter to amplify signalspassed thereby;

a comparator circuit including a first input connected to saidamplifier, a second input, and a reference level circuit connected tosaid second input, said comparator circuit being operable to providefirst and second signals when the signal level at said first input isabove and below, respectively, the reference level;

an inverter connected to said comparator circuit to invert the first andsecond signals;

first and second indicating means including first and second drivers andfirst and second lamps connected to respective drivers for identifyingdefective and sound igniters, respectively;

a latching circuit including a first input and first and second outputs,said first input connected to said inverter, said first and secondoutputs connected to said first and second drivers, respectively, saidlatching circuit responsive to the inverted first and second signals tooperate said first and second drivers, respectively.

6. In an apparatus for testing electrical resistance type igniterswherein an operating voltage is applied to an igniter to effect thegeneration of high frequency noise by a defective igniter, an impedanceis connected in circuit with the igniter to sample signals developed bythe igniter, and a signal level detection circuit is connectedto theimpedance for determining whether the sampled signals represent adefective igniter or a sound igniter, the improvement comprising:

means for increasing the signal level of the sampled signals, whereinthe impedance is an inductor connected in series with the igniter.

7. In an apparatus for testing electrical resistance type igniterswherein an operating voltage is applied to 0 an igniter to effect thegeneration of high frequency noise by a defective igniter. an impedanceis connected in circuit with the igniter to sample signals developed bythe igniter, and a signal level detection circuit is connected to theimpedance for determining whether the sampled signals represent adefective igniter or a sound igniter, the improvement comprising:

means for increasing the signal level of the sampled signals, whereinthe impedance is a radio frequency transformer including a primarywinding connected in series with the igniter and a secondary windingconnected to the signal level detection circuit.

8. Apparatus for testing for a faulty condition of an electricalresistance type igniter, comprising:

means for providing power to an igniter under test to cause the 'gener'ation of high frequency noise from a faulty igniter,

detecting means connected to the igniter under test for detecting thepresence of high frequency noise generated by a faulty igniter, saiddetecting means including an inductor for sampling the high frequencynoise, and

signal means responsive to the detecting means for indicating a faultycondition of the igniter under test. 9. Apparatus for testing for afaulty condition of an electrical resistance type igniter, comprising:

means for providing power to an igniter under test to cause thegeneration of high frequency noise from a faulty igniter,

detecting means responsive to the igniter under test for detecting thepresence of high frequency noise generated by a faulty igniter, saiddetecting means including a high frequency transformer for sampling thehigh frequency noise, and

signal means responsive to the detecting means for indicating a faultycondition of the igniter under test.

10. Apparatus for testing for a faulty condition of an electricalresistance type igniter, said apparatus comprising:

means for providing power to an igniter under test to cause thegeneration of high frequency noise from a faulty igniter; detectingmeans responsive to the igniter under test for detecting the presence ofhigh frequency noise, said detecting means including filter means forpassing only high frequency noise, a high frequency transformer forcoupling the high frequency noise to said filter means, amplificationmeans electrically connected to the filter means for amplifying the highfrequency noise passed by the filter means,

and comparator means electrically connected to igniter under test.

1. Apparatus for testing an electrical resistance type igniter foroperational defects, comprising: means for applying an operating voltageto the igniter to cause the generation of high frequency noise by theigniter if it is defective; an inductive impedance connected to theigniter for sampling signals developed by the igniter; filter meansconnected to said inductive impedance for passing high frequency noise;amplifying means connected to said filter means for amplifying thesignal received therefrom; signal level detector means connected to saidamplifying means for desensitizing the circuit with respect to noisesignals below a reference level; and signal means connected to saidlevel detector means and operative to indicate a defective igniter. 2.Apparatus according to claim 1, wherein said inductive impedancecomprises an inductor connected in series with said igniter. 3.Apparatus according to claim 1, wherein said inductive impedancecomprises a radio frequency transformer including a primary windingconnected to the igniter and a secondary winding connected to saidfilter means.
 4. Apparatus for testing electrical resistance typeigniters for operational defects comprising: means for connecting anigniter to an electrical supply for providing an operational voltage tothe igniter, a defective igniter being responsive to the operationalvoltage to generate high frequency noise; a radio frequency transformerfor sampling signals developed across the igniter, said transformerincluding a primary winding connected to the igniter and a secondarywinding; a high pass filter connected to said secondary winding forpassing hIgh frequency noise; an amplifier connected to said high passfilter to amplify signals passed thereby; a comparator circuit includinga first input connected to said amplifier, a second input, and areference level circuit connected to said second input, said comparatorcircuit being operable to provide first and second signals when thesignal level at said first input is above and below, respectively, thereference levels; an inverter connected to said comparator circuit toinvert the first and second signals; first and second indicating meansincluding first and second drivers and first and second lamps connectedto respective drivers for identifying defective and sound igniters,respectively; a latching circuit including a first input and first andsecond outputs, said first input connected to said inverter, said firstand second outputs connected to said first and second drivers,respectively, said latching circuit being responsive to the invertedfirst and second signals to operate said first and second drivers,respectively.
 5. Apparatus for testing electrical resistance typeigniters for operational defects, comprising: means for connecting anigniter to an electrical supply for providing an operational voltage tothe igniter, a defective igniter being responsive to the operationalvoltage to generate high frequency noise; an inductor connected inseries with the igniter to sample signals developed across the igniter;a high pass filter connected to said inductor for passing high frequencynoise; an amplifier connected to said high pass filter to amplifysignals passed thereby; a comparator circuit including a first inputconnected to said amplifier, a second input, and a reference levelcircuit connected to said second input, said comparator circuit beingoperable to provide first and second signals when the signal level atsaid first input is above and below, respectively, the reference level;an inverter connected to said comparator circuit to invert the first andsecond signals; first and second indicating means including first andsecond drivers and first and second lamps connected to respectivedrivers for identifying defective and sound igniters, respectively; alatching circuit including a first input and first and second outputs,said first input connected to said inverter, said first and secondoutputs connected to said first and second drivers, respectively, saidlatching circuit responsive to the inverted first and second signals tooperate said first and second drivers, respectively.
 6. In an apparatusfor testing electrical resistance type igniters wherein an operatingvoltage is applied to an igniter to effect the generation of highfrequency noise by a defective igniter, an impedance is connected incircuit with the igniter to sample signals developed by the igniter, anda signal level detection circuit is connected to the impedance fordetermining whether the sampled signals represent a defective igniter ora sound igniter, the improvement comprising: means for increasing thesignal level of the sampled signals, wherein the impedance is aninductor connected in series with the igniter.
 7. In an apparatus fortesting electrical resistance type igniters wherein an operating voltageis applied to an igniter to effect the generation of high frequencynoise by a defective igniter, an impedance is connected in circuit withthe igniter to sample signals developed by the igniter, and a signallevel detection circuit is connected to the impedance for determiningwhether the sampled signals represent a defective igniter or a soundigniter, the improvement comprising: means for increasing the signallevel of the sampled signals, wherein the impedance is a radio frequencytransformer including a primary winding connected in series with theigniter and a secondary winding connected to the signal level detectioncircuit.
 8. Apparatus for testing for a faulty condItion of anelectrical resistance type igniter, comprising: means for providingpower to an igniter under test to cause the generation of high frequencynoise from a faulty igniter, detecting means connected to the igniterunder test for detecting the presence of high frequency noise generatedby a faulty igniter, said detecting means including an inductor forsampling the high frequency noise, and signal means responsive to thedetecting means for indicating a faulty condition of the igniter undertest.
 9. Apparatus for testing for a faulty condition of an electricalresistance type igniter, comprising: means for providing power to anigniter under test to cause the generation of high frequency noise froma faulty igniter, detecting means responsive to the igniter under testfor detecting the presence of high frequency noise generated by a faultyigniter, said detecting means including a high frequency transformer forsampling the high frequency noise, and signal means responsive to thedetecting means for indicating a faulty condition of the igniter undertest.
 10. Apparatus for testing for a faulty condition of an electricalresistance type igniter, said apparatus comprising: means for providingpower to an igniter under test to cause the generation of high frequencynoise from a faulty igniter; detecting means responsive to the igniterunder test for detecting the presence of high frequency noise, saiddetecting means including filter means for passing only high frequencynoise, a high frequency transformer for coupling the high frequencynoise to said filter means, amplification means electrically connectedto the filter means for amplifying the high frequency noise passed bythe filter means, and comparator means electrically connected to theamplification means for providing a reference signal level, comparingthe level of the amplified high frequency noise with the referencesignal level, and passing only amplified high frequency noise above thereference level; and signal means responsive to the detecting means forindicating a faulty condition of the igniter under test, said signalmeans comprising switch means including a memory circuit electricallyconnected to the comparator means and responsive to the comparatormeans, and indicator means responsive to the switch means fordemonstrating a faulty condition of the igniter under test.